Radiation sources having a high luminance are required for projection applications. Furthermore, an emission angle of ≦30° is desired since optical systems generally have a numerical aperture ≦0.5 and an irradiation within this emission angle can thus be used.
I. Schnitzer et al., Appl. Phys. Lett. 63(16), Oct. 18, 1993, 2174-2176 describes the basic principle of a thin-film light-emitting diode chip. A thin-film light-emitting diode chip is to a good approximation a Lambertian surface emitter. Although a thin-film light-emitting diode chip is suitable for projection applications on account of the emission characteristic, conventional thin-film light-emitting diode chips usually have a layer structure having an active layer whose amount of radiation is limited by the current intensity. This is because the current density in the active layer should not exceed a maximum current density since otherwise there is the risk of excessive aging effects disadvantageously shortening the lifetime of the LED semiconductor body.